Ljusströmmen

Ljusströmmen, often translated as luminous flux, is a fundamental photometric quantity that measures the perceived power of light. It quantifies the total amount of visible light emitted by a source or passing through a surface. Unlike radiant flux, which measures the total energy of electromagnetic radiation, luminous flux specifically accounts for the sensitivity of the human eye to different wavelengths of light. The unit of luminous flux is the lumen (lm).

The perception of brightness is subjective, and this is where luminous flux comes into play. The human eye is not equally sensitive to all colors. It is most sensitive to light in the green-yellow region of the spectrum (around 555 nanometers) and less sensitive to colors at the extreme ends, such as violet and red. Luminous flux incorporates this spectral sensitivity through a function known as the luminosity function, which assigns a weight to each wavelength based on how bright it appears to the average human observer.

Luminous flux is an important metric for comparing the brightness of different light sources. For example, a 60-watt incandescent light bulb might produce a certain number of lumens, while a more energy-efficient LED bulb of the same wattage might produce significantly more lumens, indicating it is a brighter light source. It is crucial for applications ranging from lighting design and illumination engineering to evaluating the performance of displays and projectors.